Not happening since it doesn't have Thunderbolt
Steam Deck's USB C is just a connector. What that port can do depends on every device’s implementation. The steam deck is just standard regular USB C with DisplayPort, charging, and data
Maybe in the future Valve will release Steam Deck 2 (or just Steam Deck gen 2)
But you'll never know, the modding community has done a lot of cool things, they might get the Steam Deck to work with an eGPU